Demystifying ocean acidification and biodiversity impacts

instead of global warming these days we talk about global change and ocean acidification kind of worked its way into the fabric of this change making it possible for us to look at the problem of global change in a more expansive way than the more simplistic idea of global warming but what is ocean acidification and how exactly does it affect our topic of interest biodiversity first we need to look at the cause of ocean acidification in order to understand what it actually is and what it means to biodiversity essentially if you talk about this big cloud

this puff of co2 that's produced by human activity 30 to 40 percent almost half of that cloud ends up dissolved in the ocean the rest stays in the atmosphere or it's incorporated into living things in some form or another usually as plant material or the bodies of other producers but the huge amount of co2 that gets dissolved in the oceans is definitely going to be doing something the added co2 in the ocean causes an increase in acidity acidity is measured by something called pH and it's worth talking a little bit about pH for a moment

a couple of things to note about the pH scale it goes from zero to 14 where zero is highly acidic and 14 is highly alkaline also called highly basic a pH of 7 is neutral like distilled water so if you increase acidity the pH is dropping and if you increase alkalinity the pH is going up note that the pH scale is logarithmic which means that each step is a factor of 10 if you go from a pH of 6 to something slightly less alkaline that is more acidic at a pH of 5 you're actually increasing

the acidity 10 times going from pH 6 to pH 4 it's more acidic by a factor of 10 times 10 which means a hundred times more acidic most importantly pH is a measure of potential that's where the P in pH comes from the power or potential of a liquid to make charged hydrogen atoms or ions think of pH as potential H or power of hydrogen ions we'll see in a moment why the power of such a tiny thing as a hydrogen ion is so crucial first let's look at this problem of introducing carbon dioxide to

seawater over the industrial period between about 1750 1 and the early 1990s the surface ocean pH decreased from about eight point two five to eight point one four that doesn't sound like a lot but remember we're talking about an average for the entire global ocean over the globe and it's logarithmic so we're actually talking about a 30% increase in hydrogen ion concentration in the ocean we've got co2 in the atmosphere that's going into the water the co2 breaks down we have a chemical reaction where the co2 plus the water leads to carbonic acid the process

looks like this when you have the carbonic acid in the water a couple of things happen each carbonic acid molecule can release one of its hydrogen ions to make something called a bicarbonate and a bicarbonate molecule can further breakdown into a carbonate ion the big issue here is you get both of these molecules bicarbonate and carbonate by losing hydrogen ions which are now zipping around freely in the water and remember what we said about hydrogen ions they're going to increase the acidity of the water that's the key point through the addition of co2 you set

up a chain of events that results in these powerful little hydrogen ions being set free as the active ingredient or the culprit in the damage that acids can do its we're talking about this global process in terms of rate it's not so much that the pH levels are changing but they're changing faster than anything we've seen for a very long time the current rates of acidification are very similar to those during an enormous greenhouse event that occurred at the paleocene-eocene boundary 55 million years ago and that time was marked by huge extinctions at very fundamental

levels of ecosystem production particularly in the deep-sea geologic history tells us that biodiversity can be threatened by exposure to increased acidity in the oceans there's a huge range of harmful consequences including drops in metabolic rate or drops an immune response to other organisms such as parasites or bacteria that are in the environment and we know that drops in pH can cause destruction of coral by triggering chemical reactions that result in an overall drop of the amount of carbonate ions available okay so what does that mean well it means a bit more chemistry many organisms that

live in the ocean use a very special building material calcium carbonate which is dissolved in seawater and it's made by this reaction add calcium atoms to carbonate ions and you make calcium carbonate a material that goes into the skeletons of organisms that live in the sea such as corals and mollusks and crabs they're very dependent on calcium carbonate unfortunately these free carbonate ions are also recombining with those busy very reactive hydrogen ions to make more bicarbonate so this reduces the available calcium carbonate that organisms would otherwise be able to use and that means that organisms

with a calcium carbonate are going to have trouble maintaining their skeletons simply because they can't get enough of the calcium carbonate to grow or repair their shells and skeletons it turns out that it's not just corals mollusks and crabs that are affected single-celled organisms called foraminifera and Coco Litha fors which are close to the base of the food web and terribly important in marine ecosystems are among the most effective if you put a foraminifera nor 4m under a microscope they look like little spirals and funny shaped boxes they're fantastic things to look at forearms are

like little single-celled amoebas at make shells their metabolism and ability to make those shells is deeply affected by pH levels in the ocean now Coco Litha fors are really interesting somewhat mysterious single-celled algae that also take up calcium carbonate from the ocean to make a coke Olaf LIF means rock and Coco roughly means berry shaped so these organisms are shaped like tiny fruit but with a rocky covering not everyone knows about these but now you do because they're plants they are really important as phytoplankton producers in ocean ecosystems no one's too sure why they make

their calcium carbonate coverings but the mere fact that they are making their calcium carbonate shells means that they're also going to be deeply affected by decreasing oceanic pH and there have always been lots and lots of cocoa Luther fours the White Cliffs of Dover are made up almost entirely of fossil cocoa le'ts cocoa lucifer's produce a chemical that contributes to the formation of clouds some scientists even think that threatening the existence of cocoa Luther fours could result in a reduction in cloud cover over the oceans reducing the reflectivity of the earth and thereby increasing the

rate of global warming as I mentioned bigger things like corals and crabs and snails and clams will also some issues with their ability to secrete calcium carbonate they depends so much on that scientists have run experiments in which increasing the amount of co2 in the air above a tank of seawater can actually increase the rate at which the skeletons of some of these forms will dissolve now notice I said some it's variable but we're seeing some effects in almost every major group of organisms that we've looked at so far even in starfish and sea urchins

which have protective skin over their entire bodies they actually have an internal skeleton like fish or you or me but even those have problems particularly in larval stages and these larvae form a huge part of the plankton and remember how crucial plankton are to food webs in the sea even for organisms that don't have calcium carbonate skeletons and shells increased acidity can be a problem hypercapnia which is an actual excess of co2 and the body fluids of organisms can happen in things like fish or squid and mess with their immune responses excess co2 can even

make it difficult for baby clownfish to distinguish among the odors of friends and foes and interfere with sensory mechanisms or even the ability to hear predators coming the latter is kind of interesting because you can get changes in the acoustic properties of seawater by changing its chemistry and that has huge implications for any animal that uses echolocation for example co2 increases ocean noise which is already getting noisier all the time through other human activities more acidic environments can interfere with the construction of things like ear bones and balance organs such as what are known as

stato lists tiny little stones that squid make and hold in special chambers in their bodies stata lists allow squid to sense pressure and changes in direction and movement and this just illustrates how little we know things have unusual kinds of cascading effects that you might not think of over and above this inability to make calcium carbonate skeletons from seawater here's another example that has a complicated story like land plants sea grasses do a bit better in building their bodies when co2 levels are increased and sea grasses are really important they're valuable feeding and spawning sites

for a variety of species so if you enhance the growth of sea grasses maybe you're doing something good but what we don't know is if those local benefits of better sea grass growth will be outweighed by the wider disruption to the marine food chain as a whole and what that means for biodiversity these are all pretty complicated things we don't really know what the long-term or even short-term interplay of all these different factors is going to be we definitely need some focused research on these topics but we do know that ocean acidification is certainly mostly

bad news it's a global problem and we're going to need to start talking about global solutions as soon as possible